Focal articular cartilage defects of the knee are not uncommon consequences of injuries from sports, work or activities of daily living. Arthroscopic studies have estimated the occurrence of near full thickness lesions, full thickness lesions or full thickness with boney involvement lesions greater than 1 cm2 to be in the range of 6% of all surgical procedures in the knee. These types of articular cartilage defects may cause pain, swelling and/or knee locking and thus diminish the individual's overall quality of life. The size (area dimensions), depth (partial cartilage tissue to boney involvement), containment, co-morbidities (e.g., ACL tear, meniscal tear, and malalignment) and region of a defect will influence the procedure used by surgeons. Currently, for focal defects smaller than (<) 2.5 cm2, the subject and surgeon have few options: debridement (chondroplasty), marrow stimulation (micro-fracture, abrasionoplasty, or subchondral drilling), or autograft osteochondral plugs (OATS, COR, mosaicoplasty). For defects greater than (>) 2.5 cm2, the options are allograft osteochondral plugs or autologous cultured chondrocytes (e.g. Carticel® in the United States). While these procedures show significant rates of clinical success in the short and medium term, they each have limitations ranging from the quality of the cartilage repair to the cost and complexity of surgical procedures. Additionally, some of the procedures themselves create defects (i.e. OATS) either as a direct result of the primary procedure or through second site morbidity caused by the recovery of the patient's own tissue.
The surfaces of joints that face the joint cavity are covered with a mechanically robust connective tissue layer called chondral surface or cartilage layer. Underneath the cartilage layer is a cancellous bone termed subchondral bone. The chondral surface or cartilage layer is the primary functional surface of joints such as the knee, elbow, or shoulder. The cartilage cushions shock, carries the compressive loads placed on the joint, and allows for smooth and controlled movement between the bones in the joint. The subchondral bone supports the cartilage layer by providing blood flow, nutrients and structural integrity.